Field of the Invention
The present invention relates to a quartz crystal unit comprising a quartz crystal tuning fork resonator capable of vibrating in a flexural mode, a case and a lid, and to a method of manufacturing the quartz crystal unit.
Quartz crystal units with a tuning fork, quartz crystal resonator which vibrates in flexural mode are widely used as a time standard in consumer products, wearable equipment and communication equipment (such as wristwatches, cellular phones, and pagers). Recently, because of miniaturization and the light weight nature of these products, a smaller quartz crystal unit with a smaller flexural mode, tuning fork, quartz crystal resonator is required with a small series resistance, a high quality factor and a high frequency stability.
FIG. 15(a) and FIG. 15(b) show a plan view and a side view of a quartz crystal unit 101 with the conventional flexural mode, tuning fork, quartz crystal resonator 100. The resonator 100 comprises tuning fork tines 102, 103 and tuning fork base 104. The base 104 is mounted at a mounting portion 106 of a case 105 by adhesives 107, 108 or solder. Also, electrodes 109 and 110 are disposed on the mounting portion 106 and two electrode terminals are constructed. In addition, the case 105 and the lid 111 are connected via a metal 112. The conventional quartz crystal unit is constructed like this, and it is also needed to obtain a miniature tuning fork, quartz crystal resonator with a high frequency stability to obtain a miniature quartz crystal unit with a high time accuracy.
It is, however, impossible to obtain a miniature quartz crystal unit with a conventional miniaturized, flexural mode, tuning fork, quartz crystal resonator with a small series resistance, a high quality factor and a high frequency stability. When miniaturizing the conventional flexural mode, tuning fork, quartz crystal, resonator shown in FIG. 16 (which has electrodes on the obverse faces 203, 207, reverse faces 204, 208 and the four sides 205, 206, 209, 210 of each tuning fork tine, as also shown in FIG. 17xe2x80x94a cross-sectional view of tuning fork tines of FIG. 16), it has a smaller electromechanical transformation efficiency because the resonator shape and the electrode construction provide a small electric field (i.e. Ex becomes small), as a result of which the resonator has a large series resistance, a reduced quality factor and a low frequency stability. In FIG. 16, the conventional tuning fork resonator 100 is shown with tuning fork tines 102, 103 and tuning fork base 104.
Moreover, for example, Japanese Patent Nos. P56-65517 and P2000-223992A and International Patent No. WO 00/44092 teach grooves and electrodes constructed at tuning fork tines of a flexural mode, tuning fork, quartz crystal resonator. However, they teach nothing about a quartz crystal unit of the present invention having novel shape, novel electrode construction and figure of merit M for a flexural mode, tuning fork, quartz crystal resonator, and also, teach nothing about a method for manufacturing the quartz crystal unit of the present invention.
It is, therefore, an object of embodiments of the present invention to provide a quartz crystal unit with a resonator which overcomes the above problems.
The present invention relate to the shape and electrode construction of a flexural mode, tuning fork, quartz crystal resonator which is housed in a case, and in particular, a novel shape and electrode construction for a flexural mode, tuning fork, quartz crystal resonator available for consumer products and communication equipment requiring miniaturized, high accuracy, shock proof and low priced quartz crystal units.
It is an object of the present invention to provide a quartz crystal unit with a miniature flexural mode, tuning fork, quartz crystal resonator with a small series resistance R1 and a high quality factor Q.
It is an another object of the present invention to provide a quartz crystal unit with a flexural mode, tuning fork, quartz crystal resonator which is capable of vibrating in a fundamental mode vibration with a high frequency stability which gives a high time accuracy.
It is a further object of the present invention to provide a method for manufacturing a quartz crystal unit.
According to one aspect of the present invention, there is provided a quartz crystal unit with a tuning fork, quartz crystal resonator capable of vibrating in flexural mode comprising; tuning fork tines, and a tuning fork base, at least one groove provided in the central line portion of each of said tuning fork tines, at least one first electrode provided inside each groove, at least one second electrode provided on the sides of said tuning fork tines, and for each tine said at least one second electrode having an opposite electrical polarity to said at least one first electrode.
According to a second aspect of the present invention there is provided a quartz crystal unit with a tuning fork, quartz crystal resonator capable of vibrating in flexural mode comprising; tuning fork tines, and a tuning fork base, a plurality of step difference portions provided at said tuning fork tines along the direction of length thereof, at least two of the plurality of step difference portions being connected via at least one step portion, first electrodes on the step difference portions, second electrodes disposed opposite to the first electrodes on the sides of said tuning fork tines, and said first and second electrodes being of opposite electrical polarity.
According to a third aspect of the present invention there is provided a method for manufacturing a quartz crystal unit comprising; a flexural mode, tuning fork, quartz crystal resonator, a case and a lid.
Embodiments of the present invention may provide a high electromechanical transformation efficiency.
Embodiments of the present invention use grooves or step differences and an electrode construction arranged on the tuning fork tines and/or tuning fork base of a flexural mode, tuning fork, quartz crystal resonator.
Preferably, the resonator has grooves including the central line of the central portions for each tuning fork tine and the electrodes disposed inside the grooves and disposed on the sides of each tuning fork tine. Alternatively or additionally the grooves may be arranged on the tuning fork base and the electrodes disposed inside the grooves.
Preferably, the resonator has a step difference constructed at tuning fork tines and/or tuning fork base and electrodes disposed on the step difference portions.
For a better understanding of the present invention, and as to how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings.